Fig. 2. Expression of Wnt signaling genes and Wnt reporter activity. (A-D) ISH for chick Wnt2b. Wnt2b signal was observed exclusively in the SE (arrowheads) at the OV stages (A,B), and in the RPE (arrow) and the peripheral tip of the retina (white arrowhead), in addition to SE (black arrowhead), at the OC stage (C,D). (E-H) ISH for Lef1 (E,G) and Chx10 (F,H). Stages are invaginating OV (E,F) and early OC (G,H). White lines in A,B,E,F,H outline the OV and OC. Arrowheads in E,F indicate the dorsal OV. Arrows in G,H indicate the peripheral OC. (I) Structure of the Wnt reporter SuperTopAP and the mutant reporter SuperFopAP. (J,K) AP staining of retinal sections electroporated with SuperTopAP and assayed at the OV (J) and early OC (K) stages. Note that the anterior OV (blue line), the anlage for the central retina, does not show Wnt activity, whereas the posterior/dorsal OV (red and green), the anlagen for RPE and ciliary/iris epithelia, respectively, show strong AP staining. Inset in K' shows a close-up of the central retinal cells showing weak Wnt activity in some of the cells adjacent to the RPE. (L) AP staining of a retinal section electroporated with the mutant Wnt reporter SuperFopAP. (M-O) Co-electroporation of pMIW III:GFP shows the areas of reporter DNA delivery in sections corresponding to panels L,J and K, respectively. Note that the areas with a high AP signal have reduced GFP signal due to quenching of the immunofluorescence. Di, diencephalons; Lv, lens vesicle; Lp, lens placode. Dorsal side is up. Scale bars: 150 µm.